The HPV Serology Laboratory leads an initiative to standardize and harmonize human papillomavirus serology assays

The HPV Serology Laboratory is leading a global partnership initiative aiming for standardization and harmonization of current serology assay platforms being used to assess immune responses to HPV vaccines. Serology standardization is particularly important given the increasing number of immunobridging trials relying on serology data for approval of new vaccine dosing schedules or vaccine formulations. The initiative was established in 2017 to enable comparisons of data between different vaccines and relevant studies as well as expedite the implementation of new vaccines and vaccine indications. The HPV Serology Laboratory has held or attended several meetings with partnering laboratories, including international meetings in 2017, 2018, and 2021.

Briefly, in response to the initial convention, the HPV Serology Laboratory (HPVSL) at FNLCR was established in January 2017 to address this challenge, in partnership with the National Cancer Institute and the Bill & Melinda Gates Foundation. A follow up meeting at the 32nd International Papillomavirus Conference in Sydney, Australia from October 2 to 6, 2018, was convened to discuss the progress of main aims, challenges, and some of the future needs. The outcomes of this meeting included definition of the primary mission of the initiative, which was to enable comparisons of data between different vaccines and different relevant studies, as well as expedite the implementation of new vaccines and vaccine indications. The specific aims to drive these goals include: 1. The development of a qualified secondary assay standard and a bank of serum specimens to use as assay proficiency panels for 9 HPV types (HPV-6/11/16/18/31/33/45/52/58) included in the licensed HPV vaccines.
2. The production of qualified reference reagents (HPV Virus-Like Particles) by establishing a set of criteria or guidelines for qualification.
3. The development of a validated multiplex serology assay to enable immunogenicity monitoring in HPV vaccine trials.
4. The promotion of the use of standards through platforms such as meetings, publications, data, and protocol sharing.
We herein briefly describe the progress to each of the 4 objectives as well as provide the links to all currently developed standard operating procedures (SOPs).
First, HPVSL was able to generate qualified secondary standards calibrated against HPV-16 and HPV-18 WHO International Standards (IS). For this effort, 144 human serum samples were obtained from various sample providers, and each sample was screened and categorized depending on the specific antibody response for each HPV type. Moreover, an HPV assay proficiency panel of 80 samples covering a wide range of HPV antibody responses was established. Currently, the proficiency panel has been distributed and tested by 10 laboratories with their respective antibody binding or pseudovirion-based neutralization assays.
Second, the production of the first lot of qualified VLPs for multiple HPV types (HPV-6/ 11/16/18/31/33/45/52/58) was completed at the time of the follow up meeting in 2018. These reagents will be available for reference use in assays in respective laboratories.
Third, a high-throughput Luminex bead-based 9-plex immunoassay was developed and a validation plan for the HPV-16 and HPV-18 ELISAs and multiplex assay was drafted. To date, the 9-plex assay validation has been completed and guidance documents for data processing and analyses are under development.
Lastly, efforts have been made to promote the development and use of standards, SOPs, and data (Table 1). Up to 8 material transfer agreements had been established at the time of the follow up meeting in 2018. Protocol and data sharing with the greater HPV serology community are now enabled by a dedicated FNL HPV Serology Laboratory website, where investigators and researchers can access serology laboratory SOPs, guidance documents for VLP production and qualification, and multiplex assay validation protocol.
As part of this initiative, the HPVSL has been collaborating with NIBSC and WHO to develop International Standards for the remaining HPV types in the nonavalent vaccine, including HPV high-risk types (HPV-31, HPV-33, HPV-45, HPV-52, and HPV-58) and low-risk types (HPV-6 and HPV-11). These standards were recently approved by WHO and are now available for request through NIBSC's website (https://www.nibsc.org/products/brm_product_catalogue/sub_ category_listing.aspx?category=Vaccines&subcategory=Human%20Papillomavirus). Future directions discussed by the initiative consisted of (1) implementation of highthroughput HPV antibody testing using Good Clinical Laboratory Practices (GCLP) to support ongoing and future vaccine immunogenicity trials; and (2) development of an HPV Vaccine Trial Network of laboratories involved in the testing of HPV vaccines to expand training capability as well as establish an Assay Proficiency Panel Program.
In June 2021, a virtual meeting was held on June 29 to 30, 2021, to review progress of the standardization initiative thus far and to bridge scientific gaps and outstanding questions. The main aims and outcomes of the meeting were to discuss: (1) standardization of assays and reagents; (2) International Standard Calibration procedures; (3) assay cut-off values; (4) current immunobridging clinical trials; (5) gaps and challenges in standardization of HPV serology. A total of 119 scientists and clinicians from 13 countries, representing 36 institutions and industries, participated in the meeting to update the community on the progress on the objectives of the initiative. Participants also reported on advancements made by the HPV serology community in exploring and advancing with new vaccine dosing schedules or vaccine formulations. A report summarizing the meeting has been recently published [9].